Three-dimensional eye rotation measurements will be made in normal subjects and in strabismus patients before and after necessary surgery. An objective photographic method and a psycho-physical after-image alignment task will supply the basic data. What is new is an analysis which gives a true value of torsion in any gaze position by taking the raw data and rigorously describing the orientation of the eye in terms of a rotation matrix, 3 precisely defined spherical angles, or an axis and extent of a rotation. This provides a general, convenient, and complete way to specify the rotational state of the eye in the head as well as providing the proper mathematical language to analyze the rotations of the eye in terms of forces acting in 3 dimensions. The change in cyclo-rotation will be measured for each eye as it looks in different gaze directions for normal subjects and then for patients before and after surgery. The measurements will be conducted to provide: 1) an exact description of the nature of a specific disorder in three-dimensional geometric terms; 2) an exact characterization of the effects of surgery which correct for or induce torsion; 3) a quantitative way to check theoretical formulations of the cooperative actions of the 6 extra-ocular muscles.